The present invention relates to a magneto-resistive effect type head for reading an information signal from a magnetic medium and more particularly to a magneto-resistive effect type head having a structure capable of preventing the destruction of the insulation layer by static electricity.
With the down-sizing and performance improvement of the magnetic recording apparatuses in recent years, the magneto-resistive effect type head (hereafter referred to as the MR head) utilizing the magneto-resistive effect is used as the head for reading an information signal from the magnetic medium. FIG. 1 shows an example of the MR head. The MR head has a composite structure including a recording head 1 utilizing electromagnetic induction to write information and a reproducing head 2 utilizing a magneto-resistive effect (MR) or a giant magneto-resistive effect (GMR) to read the information signal from the magnetic medium.
FIG. 2 shows an example of the reproducing head in a view facing the magnetic medium. The reproducing head includes an MR sensor 30, electrode layers 40, a lower insulating layer 20, and an upper insulating layer 50, which are all disposed between a lower shield layer 10 and an upper shield layer 60. Generally, the bias layers 45 to apply a vertical bias magnetic field to the MR sensor 30 are provided on both sides of the MR sensor 30 (Normally, the bias layers and the electrode layer are formed successively).
The lower insulating layer 20 and the upper insulating layer 50 performs the function to magnetically and electrically isolate the MR sensor 30 from the lower shield layer 10 and the upper shield layer 60. As the material for the insulating layers, an aluminum oxide (alumina) film is generally used which is non-magnetic and superior in electrical insulating properties. The space where the MR sensor 30 is disposed between the lower shield layer 10 and the upper shield layer 60 is defined as a gap length GL. In a magnetic recording apparatus, the gap length GL is an important parameter related to bit length.
Magnetic recording apparatuses are becoming smaller and improving in performance year by year and accordingly the gap length GL of the reproducing head to read information is becoming narrower. In consequence, the trend of the lower insulating layer 20 and the upper insulating layer 50 has been toward a thinner film thickness.
As the lower insulating layer 20 and the upper insulating layer 50 become narrower, those insulating layers are liable to dielectric breakdown due to static electricity produced in the magnetic head manufacturing and assembling processes. Measures have been taken to prevent static electricity from accumulating in the magnetic head manufacturing and assembling processes. However, it is impossible to achieve complete prevention of dielectric breakdown caused by static electricity in those processes. Therefore, the structure of the magnetic head must be so formed as not to suffer dielectric breakdown even if static electricity is produced to some extent.
JP-A-07-65324 (U.S. Pat. No. 5,539,598) and JP-A-07-65330 disclose methods in which the shield layer and the electrode layer are shorted electrically. Moreover, JP-A-08-22172 (U.S. Pat. No. 5,375,022) reveals a method in which the shield layer and the electrode layer are connected by a high-resistivity magnetic material. Those methods, when static electricity occurs, bring the MR sensor 30 and the shield layer to the same potential when static electricity occurs to thereby prevent a breakdown of the insulating layers between the MR sensor and the shield layers. However, there is a decrease in output because the sense current splits from the electrode layer and flows to the shield layers even when the magnetic head is operating in the reproducing apparatus.
An object of the present invention is to provide a magneto-resistive effect type head of a structure capable of preventing a breakdown of the insulating layers between the MR sensor and the shield layers attributable to the occurrence of static electricity even when the gap length is made narrow.
Another object of the present invention is to provide a magneto-resistive effect type head of a structure in which the sense current does not shunt from the electrode layer and flows into the shield layers even when the magnetic head according to the present invention is mounted in a magnetic recording apparatus as shown in FIG. 9 and put into operation.
In the magneto-resistive effect type according to the present invention, the portions of the insulating films in which the MR sensor and the lower and upper shield layers do not face each other are formed by an insulating film with a lower resistivity than the other portions of the insulating films in which the MR sensor and the lower and upper shield layers face each other.
According to an aspect of the present invention, a magneto-resistive effect type head comprises between a lower shield layer and an upper shield layer:
an MR sensor including a thin film having at least a magneto-resistive effect or a gigantic magneto-resistive effect,
bias layers for applying a longitudinal bias magnetic field to the MR sensor, and
electrode layers for supplying a detection current to the MR sensor, and
a lower insulating layer between the MR sensor and the lower shield layer and an upper insulating layer between the MR sensor and the upper shield layer, the two insulating layers being located at that part of the head which faces a magnetic medium,
wherein portions of the lower and upper insulating layers in which the MR sensor and the lower and upper shield layers do not face each other have a lower resistivity than the other portions of the lower and upper insulating layers in which the MR sensor and the lower and upper shield layers face each other.
According another aspect of the present invention, in the magneto-resistive effect type head, the lower-resistivity portions of the insulating layers in which the MR sensor and the shield layers do not face each other exclusive of the other portions of the insulating layers in which the MR sensor and the shield layers face each other may be set either between the MR sensor and the lower shielding layer or between the MR sensor and the upper shielding layer. Namely, either all over the insulating layer between the MR sensor and the lower shielding layer or all over the insulating layer between the MR sensor and the upper shielding layer is formed of an insulating film with low resistivity.
The low-resistivity portions of the insulating layer in which the MR sensor and the lower and upper shield layers do not face each other are preferably formed by a nitride or an oxy nitride of aluminium, silicon or a mixture those elements.
This low-resistivity insulating layer preferably has a characteristic that the resistivity at an applied electric field of 3 MV/cm is less than 1/1000 of the resistivity at an applied electric field of 1 MV/cm.